The present invention relates to polyurethanes designed for thermal break (urethanes used as barriers to reduce transfer of thermal or electrical energy through metal are commercially known as thermal break systems) applications and to the mixtures of polyols and/or polyamines from which they are produced.
It is known that mixtures of polyols produce polyurethanes having improved thermal stability and impact strength. (See, e.g., U.S. Pat. No. 3,558,529). However, such polyols are generally incompatible enough that they do not form homogeneous mixtures. Use of such mixtures therefore presents storage and processing problems. For example, after brief storage periods (e.g. from a few hours to 3 days), even polyol systems which had been thoroughly mixed separate into two phases. Intensive remixing, continuous mixing or circulation would obviously prevent such separation but such measures are not commercially desirable.
A number of other techniques for promoting storage stability and homogeneity of mixtures of incompatible polyols and/or polyamines have been disclosed. Most of these techniques require the addition of a stabilizing material. For example, U.S. Pat. No. 3,945,939 teaches the addition of inert surface-active materials (such as silica agglomerate) to the disclosed polyol mixtures. U.S. Pat. No. 4,141,85&gt;teaches addition of graft polypropylene ether glycols to polyol mixtures. U.S. Pat. No. 3,993,576 teaches that use of soluble diol compounds promotes homogeneity and storage stability. Conventional emulsifiers have also been used to stabilize mixtures of incompatible polyols. U.S. Pat. No. 4,436,841 discloses polyol mixtures to which ammonium or metal salts of C.sub.1 -C.sub.8 -monocarboxylic, polycarboxylic or hydrophilic acids have been added for stability.
U.S. Pat. No. 4,575,518 discloses homogeneous storage stable mixtures of polyols containing a small quantity of salt. The salts taught to be useful are composed of a cation from the 1st, 2nd or 3rd Main Group of the Periodic System of Elements or ammonium or mono- to tetra-alkylammonium ions and an anion which is a residue of the type formed by removing at least one proton from an acid having a K.sub.s -value of at least 10.sup.-7. However, the polyol mixtures containing these salts which are disclosed in this patent produce a solid urethane which will not adhere to a substrate such as aluminum.
The ability of a polyurethane to adhere to a metal substrate is desired in thermal break applications. It would therefore be advantageous to use a homogeneous storage stable mixture of polyols to produce a polyurethane having improved mechanical properties which could be used in a thermal break system.